In Cambodia, between 1975 and 1979, the Khmer Rouge regime caused the death of 1.8 million people, representing one-quarter of the population of Cambodia. Kaing Guek Eav, better known as Duch, was in charge at M13, a Khmer Rouge-controlled prison, for 4 years before being appointed by Angkar, to the S21 centre in Phnom Penh. As party secretary, he commanded from 1975 to 1979 the Khmer Rouge killing machine in which at least 12,280 people perished, according to the remaining archives. But how many others disappeared, "crushed and reduced to dust"? In 2009, when Duch attends his new trail, Rithy Panh asks him the long question and gets the answer.